In modern completion technology presently used for completing oil wells, it is possible to fire wireline perforating guns that may be as long as forty feet. In firing these relatively long strings of perforating guns, the shaped charges carried by the guns are typically connected to each other by a detonating cord which passes through or near the apex of each of the conically shaped charges. The primacord or detonating cord joins them all together. The detonating cord is typically fired by a detonator, or initiator, that is located at the lower end of the gun. The reason for placing a detonator at the bottom of the gun is to allow it to become disabled by well fluids, should the perforating gun have a leak. Experience has shown that firing a perforating gun which is full, or partially full, of fluid is catastrophic. Upon firing a fluid-filled gun, severe expansion, or possibly even rupturing, of the outer housings result. Thus it is possible to leave swollen housing inside the well bore, depriving the well operator from producing oil or gas from that particular zone until the housing are removed, usually by expensive fishing operations.
Particularly in the case of relatively long strings of hollow carrier perforating guns which are to be fired from below or from the lower end of the string, it has been desirable to use explosive initiators of the slapper type or exploding foil type for safety purposes. Explosive initiators of the slapper type or exploding foil initiator type are inherently safer than previously used explosive initiators or blasting caps, because a less sensitive secondary explosive may be used in initiators of this type. The relatively lower sensitivity secondary explosive used in this type of detonator requires a higher energy to cause its detonation. This is provided in the case of the exploding foil initiator by a sudden high volatge, high current pulse of electricity which is applied across a thin foil of conducting material and which causes it to violently and rapidly vaporize, and subsequently propel or slap a flyer against the secondary high explosive mixture used in the detonating cap.
Thus, the use of exploding foil initiators at the bottom end of lengthy strings of perforating guns requires the generation of a high voltage, high intensity electrical pulse or spike which must be supplied to the exploding foil or slapper type initiator in order to cause its detonation. This can present a problem, particularly since the electronic power supply typically used for providing the high volatge, high current spike is housed at the upper end of the string of perforating guns. Thus, it is necessary to conduct the high voltage, high current spike over a relatively lengthy firing line and still supply it to the exploding foil or slapper type initiator with sufficient voltage amplitude and current intensity to cause detonation of the slapper or exploding foil type detonator.
One method to deliver the necessary high voltage, high current pulse to the slapper type initiator, is by the use of coaxial cable or flat cable having a low resistance and low inductance. This cable can be connected from the power supply at the top of the string to the initiator at the lower end. However, the geometry and size requirements of the perforating guns typically used can usually prevent the use of the necessary sizes of coaxial or flat cable required to conduct the sharp pulse over a relatively long length, such as thirty or forty feet. The system and method of the present invention overcomes these problems without the use of special coaxial or flat cable.